Reminds me of the concept of data furnace: a "method of heating residential homes by running servers in them"

http://arstechnica.co.uk/business/2015/05/data-furnaces-arri...

When I was at University I stayed in a 7ft X 7ft room (because it was £40 per week) and my computer often made my room too warm, especially if I was overclocking.

Quarnot does this too (European), free heating bill. Never tested it personally though.

http://www.qarnot-computing.com/qrad

For the power consumption problem, what about only using the phone when it is connected to power and fully charged? Most people charge their phones overnight.

Plus they're at home so they have fast wifi access.